A bit patterned media (BPM), which may be the next generation of data storage media, may extend the data storage capacity of hard drive disks. As illustrated in FIG. 1f, conventional BPM may include a base 102, a storage layer 104, an intermediate layer 103, and a protective layer 106. Within the data storage layer 104, there may be a plurality of active regions 104b, each of which is used for storing a single bit of data, and one or more separators 104a for isolating each active region 104b. As each data bit is stored in each active region 104b, the capacity of the media 100 depends on the number of the active regions 104b. A media 100 with greater number of active regions 104b may store more data.
In conventional BPM, the active regions are formed during manufacturing of the media 100. This is contrary to earlier data storage media, where the active regions are formed while the data is recorded. Referring to FIG. 1a-1f, there is shown a conventional method for manufacturing BPM 100. Initially, the media 100 may comprise a base 102 and the data storage layer 104. The data storage layer 104 may contain ferromagnetic material.
First, a patterning process is performed on the media 100. In this process, a layer of resist 108 is deposited onto the data storage layer 104 (FIG. 1a). Thereafter, the resist layer 108 is patterned using a known lithographic process such as the photolithographic process, the nano-imprint lithographic process, or the direct write electron beam lithographic process. As shown in FIG. 1b, one or more portions of the data storage layer 104 are exposed after the lithographic process.
After the patterning step, an etching step may be performed. An example of the etching step may be the ion milling process. In this step, reactive ions 122 are directed toward the exposed portions of the data storage layer 104, and the ferromagnetic material from the exposed portions is removed (FIG. 1c). Meanwhile, portions of the data storage layer 104 that are not exposed are shielded by the resist 106 and remain on the media 100. When viewed from the side, the resulting media 100 may comprise columns 104b of ferromagnetic material spaced apart and isolated from each other by gaps. The columns that remain on the media 100 may ultimately form the active regions 104b. Areas between the columns (e.g. gaps) are then filled with non-magnetic material with low permeability and remanence to form the separators 104a (FIG. 1d). Thereafter, the media 100 is planarized (FIG. 1e), and a protective coating 106 is deposited onto the media 100 (FIG. 1f). The resulting media 100, as noted above, comprises a data storage layer 104 having a plurality of active regions 104b isolated by one or more non-magnetic separators 104a. 
As an improvement, a process of manufacturing BPM that incorporates ion implantation step has been proposed. This process is shown in FIG. 2a-2e. 
First, the resist layer 108 is deposited on the data storage layer 204 (FIG. 2a). The material in the data storage layer 204 may be ferromagnetic material. After depositing the resist layer 108, the resist layer 108 is patterned using one of the known lithographic processes, and portion(s) of the data storage layer 204 are exposed. Thereafter, ions 222 are directed toward the data storage layer 204. In this process, the ions 222 are implanted into the data storage layer 204. The ions 222 then convert the material in the regions 204a from ferromagnetic material to a material with low permeability and ideally no remanence to form the separators 204a (FIG. 2c). Meanwhile, material in the region 204b that is not exposed and not implanted with the ions 222 may remain ferromagnetic. The resulting data storage layer 204 may include active regions 204b, which were not exposed to the ions, and one or more separators 204a formed via exposure to the ions (FIG. 2d). The separators 204a, when formed, may isolate each active region 204b. 
After forming the active regions 204b and the separators 204a, the remaining resist layer 108 is removed, and a protective layer 106 is deposited onto the storage layer 204 (FIG. 2e).
Various approaches may be taken to form the separators 204a. In one approach, the separators 204a are formed via dilution of magnetic material. In this approach, the ferromagnetic material in the exposed regions is implanted with diluting ions, for example ion species that do not exhibit magnetic property, with sufficient dose. In the process, Curie temperature of the resulting material is reduced to room temperature or the material is no longer magnetic at room temperature. To achieve sufficient dilution, atomic concentration of ˜10% or more of the diluting ions may be needed. For a media comprising cobalt (Co) based data storage layer of 30 nm thickness, a 10% concentration implies an ion dose of approximately 3×1016/cm2. This dose may be proportional to the thickness of the storage layer and thus may be less if the data storage layer is thinner.
In another approach, the magnetic material may be converted by affecting the crystallinity or microstructure of the material in the exposed regions. The ion implantation process is an energetic process that can cause many atomic collisions. During implantation, the material in the exposed regions that is otherwise crystalline may become amorphous and/or disordered. As a result, the material may exhibit low ferromagnetism at room temperature. Meanwhile, the material in the unexposed portions next to the exposed portions may retain its original magnetic property. This approach may be effective if the original ferromagnetic layer is a multilayer that derives its magnetic properties from the interaction of very thin layers in a stack. However, this approach also may require a high ion dose. A typical ion dose necessary to amorphize/disorder a silicon substrate is 1×1015 ions/cm2 or higher. In a metal substrate, this required dose may be even higher, particularly if the implant is performed at room temperature.
Both approaches, however, have several drawbacks. One such drawback may be limited throughput caused in part by the high ion dose requirement. As noted above, each approach in forming the separator 204a requires an ion dose ranging about 1×1016-1×1017 ions/cm2. However, the beam current in a conventional ion implanter is limited due to the limitations in generating the ions. Accordingly, such a high dose will limit the throughput or increase the time the ion implantation system has to process the media. With limited throughput, the cost associated with manufacturing BPM may be high.
The throughput may also be limited in part by the resist patterning step. As noted above, the electron beam direct write patterning step may be used to pattern the resist. In this process, an electron beam is scanned along one or more directions directly write or pattern the resist. Although this process enables greater resolution, this process is very slow and it is not suitable for high throughput production.
The nano-imprint lithography process, a more efficient resist patterning process may be used to increase the throughput. This patterning process, however, does not produce resist with desired properties. For example, the maximum practical resist height achieved in the nano-imprint lithography process may be limited to about 50 nm. Such resist may not survive the subsequent high dose ion implantation process and/or adequately protect the material underneath. A portion of the resist may sputtered away during ion implantation, and portions of material outside of the exposed region (i.e. material originally under the resist 108) may be implanted with ions and also converted into the separator 204a. Accordingly, less than optimal BPM may result.
Moreover, high dose ion implantation used to form the separator 204a may also contribute to sputtering of the material in the exposed region. This sputtering effect proceeds in proportion to the total dose needed to form the separator 204a. This sputtering effect may result in a non-planar storage layer. Because the BPM manufacturing process that incorporates the ion implantation step is intended to omit the gap filling step (e.g. FIG. 1d), excessive non-planarity between the exposed region and the unexposed region may be highly undesirable.
Accordingly, a new method for manufacturing bit pattern media is needed.